(1) Field of the Invention
The present invention relates to a copying machine comprising a photosensitivity drum having an amorphous silicon type photoconductive layer formed on a photoconductive substrate. More particularly, the present invention relates to a copying machine of this type in which the image memory is effectively eliminated.
(2) Description of the Prior Art
An amorphous silicon type photoconductive layer has a high surface hardness and a sensitivity to rays on the long wavelength side and the sensitivity per se is high. Accordingly, this photoconductive layer has attracted attention as a photosensitive material for the electronic reproduction.
However, according to our research, it has been found that although amorphous silicon has the above-mentioned excellent characteristics, it is defective in that the light fatigue is relatively large in the high-speed reproduction. For example, if the operations of charging, light exposure, development, transfer and cleaning are repeated in the ordinary reproduction cycle, in case of a selenium photosensitive layer, reduction of the charge quantity at the second and subsequent stages is only about 0.5 to about 3% based on the charge quantity at the first stage and the influence of the light fatigue can be substantially neglected, but in case of amorphous silicon, reduction of the charge quantity at the second and subsequent stages is 5 to 20% based on the charge quantity at the first stage and when prints are formed at the second and subsequent stages, images of the first and precedent prints are left and formed again. That is, the problem of the image memory arises. More specifically, in the case where an amorphous silicon type photoconductive layer is used as a photosensitive material, it is a technical problem how to prevent this image memory effectively.